Image forming apparatuses conventionally have allowed double-sided printing in which images are formed on both sides of a sheet. The double-side printing is performed, for example, by forming an image on a first surface of a sheet, turning back the sheet to change the conveying direction thereof in a relay reversal unit placed between a fuser and a discharge port, and then conveying the sheet to a reversal conveyance path to reverse the front and back sides of the sheet to form an image on a second surface thereof.
If the double-sided printing as described above is used to perform double-sided printing operation successively on a plurality of sheets, so-called alternate circulation processing is performed to achieve the double-sided printing. The alternate circulation processing is a processing method for performing the double-sided printing efficiently on a plurality of sheets by forming an image on a first surface of a sheet and then forming an image on another sheet during the reversal of the front and back sides of the former sheet. In the double-sided printing with the alternate circulation processing, however, a sheet present in a reversal conveyance path may prevent the sheet having the image formed on the first surface from being introduced into the reversal conveyance path. In this case, standby processing is performed in which the sheet is caused to wait at a predetermined standby position until it can be introduced into the reversal conveyance path since the sheet in the reversal conveyance path is moved out.
In the standby processing of the sheet, the position of upstream end of the sheet in a conveying direction toward the reversal conveyance path depends on the length of the sheet. For example, a long sheet has an upstream end portion which may protrude from a relay reversal unit and extend into another unit adjacent to the relay reversal unit during the standby state. If sheet obstruction (hereinafter referred to as a jam) occurs in the state as described above in which the sheet spans the relay reversal unit and the unit adjacent to the relay reversal unit, the relay reversal unit must be pulled out of the body of the image forming apparatus to remove the sheet. At this time, the portion of the sheet that extends into the other unit may be snagged on the unit to result in damage to the sheet.